Two-photon excitation and absorption spectroscopy of gaseous and supercritical xenon

Spectroscopy of gases under high-pressure conditions is of interest in various fields such as plasma physics or astrophysics. Recently, it has also been proposed to utilize a high-pressure noble gas environment as a thermalization medium to extend the wavelength range of photon Bose-Einstein condensates to the vacuum-ultraviolet, from the presently accessible visible and near-infrared spectral regimes. In this work, we report on experimental results of two-photon spectroscopy of gaseous and supercritical xenon for pressures as high as $95 \; \text{bar}$, probing the transitions from the $5p^6$ electronic ground state to the $5p^56p$ and $5p^56p^\prime$ excited state configurations. Aiming at the exploration of possible pumping schemes for future vacuum-ultraviolet photon condensates, we have recorded degenerate two-photon excitation spectra of such dense xenon samples. In further measurements, we have investigated whether irradiation of an auxiliary light field can enhance the reabsorption of the emission on the second excimer continuum of xenon, which is subject to a large Stokes shift. To this end, absorption measurements have been conducted, driving the $5p^6 \rightarrow 5p^56p$ two-photon transitions non-degenerately.Comment: 6 pages, 6 figure

In vivo delivery of a fluorescent FPR2/ALX-targeted probe using focused ultrasound and microbubbles to image activated microglia

To image activated microglia, a small-molecule FPR2/ALX-targeted fluorescent probe was locally delivered into the brain using focused ultrasound and microbubbles. The probe did not co-localise with neurons or astrocytes but accumulated in activated microglia, making this a potential imaging tool for future drug discovery programs focused on neurological disorders.The PhDstudentships of S. V. M., T. B. and T. G. C. were funded by EPSRC Centre for Doctoral Training in Medical Imaging (EP/L015226/1) and the Centre for Neurotechnology (EP/L016737/1). Wethank Javier Cudeiro Blanco for his support and the Facility for Imaging by Light Microscopy (FILM) at Imperial College London funded by the Wellcome Trust (grant 104931/ZS/14/Z) and BBSRC (grant BB/L015129/1)

Targeting of Formyl Peptide Receptor 2 for in vivo imaging of acute vascular inflammation

© The author(s). Inflammatory conditions are associated with a variety of diseases and can significantly contribute to their pathophysiology. Neutrophils are recognised as key players in driving vascular inflammation and promoting inflammation resolution. As a result, neutrophils, and specifically their surface formyl peptide receptors (FPRs), are attractive targets for non-invasive visualization of inflammatory disease states and studying mechanistic details of the process. Methods: A small-molecule Formyl Peptide Receptor 2 (FPR2/ALX)-targeted compound was combined with two rhodamine-derived fluorescent tags to form firstly, a targeted probe (Rho-pip-C1) and secondly a targeted, pH-responsive probe (Rho-NH-C1) for in vivo applications. We tested internalization, toxicity and functional interactions with neutrophils in vitro for both compounds, as well as the fluorescence switching response of Rho-NH-C1 to neutrophil activation. Finally, in vivo imaging (fluorescent intravital microscopy [IVM]) and therapeutic efficacy studies were performed in an inflammatory mouse model. Results: In vitro studies showed that the compounds bound to human neutrophils via FPR2/ALX without causing internalisation at relevant concentrations. Additionally, the compounds did not cause toxicity or affect neutrophil functional responses (e.g. chemotaxis or transmigration). In vivo studies using IVM showed Rho-pip-C1 bound to activated neutrophils in a model of vascular inflammation. The pH-sensitive (“switchable”) version termed Rho-NH-C1 validated these findings, showing fluorescent activity only in inflammatory conditions. Conclusions: These results indicate a viable design of fluorescent probes that have the ability to detect inflammatory events by targeting activated neutrophils.British Pharmacological Society; Wilkinson Trust; EPSRC; German Research Foundation

Phytase activity in lichens

Phytase activity was investigated in 13 lichen species using a novel assay method. The work tested the hypothesis that phytase is a component of the suite of surface-bound lichen enzymes that hydrolyse simple organic forms of phosphorus (P) and nitrogen (N) deposited onto the thallus surface. Hydrolysis of inositol hexaphosphate (InsP6, the substrate for phytase) and appearance of lower-order inositol phosphates (InsP5–InsP1), the hydrolysis products, were measured by ion chromatography. Phytase activity in Evernia prunastri was compared among locations with contrasting rates of N deposition. Phytase activity was readily measurable in epiphytic lichens (e.g. 11.3 lmol InsP6 hydrolysed g-1 h-1 in Bryoria fuscescens) but low in two terricolous species tested (Cladonia portentosa and Peltigera membranacea). Phytase and phosphomonoesterase activities were positively correlated amongst species. In E. prunastri both enzyme activities were promoted by N enrichment and phytase activity was readily released into thallus washings. InsP6 was not detected in tree canopy throughfall but was present in pollen leachate. Capacity to hydrolyse InsP6 appears widespread amongst lichens potentially promoting P capture from atmospheric deposits and plant leachates, and P cycling in forest canopies. The enzyme assay used here might find wider application in studies on plant root–fungal–soil systems

Development, characterisation and in vitro evaluation of lanthanide-based FPR2/ALX-targeted imaging probes

UK Engineering and Physical Sciences Research Council (EPRSC); Royal Society Wolfson Fellowship

Assessing the quality and quantity of N deposition by total N content and the stable isotope signatures in lichen tissue

Boltersdorf S. Assessing the quality and quantity of N deposition by total N content and the stable isotope signatures in lichen tissue. Presented at the European Geosciences Union (EGU), Vienna (Austria)

Mapping agriculture-related deposition by using total nitrogen and δ15N signatures in epiphytic lichen tissue

Boltersdorf S. Mapping agriculture-related deposition by using total nitrogen and δ15N signatures in epiphytic lichen tissue. Presented at the Annual conference of German Association of Stable Isotope Research (GASIR), Villigen (Switzerland)

Luminescent compounds for targeting formyl peptide receptors

Unregulated inflammation is implicated in a variety of disease states such as stroke, cancer and neurodegenerative conditions and often the extent of inflammatory response can determine the prognosis for a particular disease state. Human neutrophils express formyl peptide receptors one (FPR1) and two (FPR2/ALX, also known as the lipoxin A4 receptor) and are known to both drive vascular inflammation and at the same time be involved in its resolution. Therefore, these receptors represent an attractive target for non-invasive visualisation of inflammation in disease states. The work within this thesis focusses on designing luminescent imaging probes that selectively tag neutrophils in an inflammatory context. To achieve this, a small-molecule FPR2/ALX ligand was chosen based on ease of synthesis, ability for further functionalisation and a dose-dependent neutrophil response observed in vitro. The targeting system was initially combined with a rhodamine-based dye and binding via the neutrophil FPR family was confirmed via pharmacological blocking. In vitro, the probe did not affect neutrophil responses and in vivo preferential uptake by neutrophils in a model of acute inflammation compared to control groups was demonstrated. Via minor synthetic alterations, a pH-responsive version based on the rhodamine spirocyclisation equilibrium was prepared (pKcycl = 3.97) and the compound was shown to be fluorescent in stimulated neutrophils in vitro but remained non-fluorescent under normal physiological conditions. By appending the same targeting group to metal chelates, compounds with long-lived luminescence signals that can be separated from cellular autofluorescence via lifetimes, were prepared. Time-resolved microscopy on activated and unactivated human neutrophils incubated with FPR2/ALX-targeted lanthanide-based compounds was performed, but high concentrations were required. A second iteration of probe design, using a Re(I) tricarbonyl motif, resulted in time-resolved images of neutrophils at lower probe concentration. Finally, a construct containing a lanthanide unit, a pH-responsive fluorophore and the targeting group was formed and the energy transfer processes in the Tb(III) analogue were investigated. The observed energy transfer provides a unique opportunity to enhance emission properties of the compound for time-resolved imaging via donor-sensitised, long-lived emission, providing an alternative radiative pathway that circumvents the formally forbidden, characteristically weak lanthanide emission.Open Acces